Pressure transfer mechanism

ABSTRACT

A pressure transfer mechanism is disclosed for applying evenly distributed pressure to a sheet of flexible photocopy paper overlying a planar surface of a photoconductor in an electrostatic photocopy image transfer station. The mechanism comprises a frame to which the photoconductor is rigidly held and a movable plate mounted for movement with respect to the frame and the photoconductor. A platen is disposed between the movable plate and the photoconductor which platen has a planar surface disposed adjacent and substantially parallel the photoconductor planar surface. A first set of compression springs is sandwiched between the movable plate and the frame. A second set of compression springs is sandwiched between the platen and the movable plate.

United States Patent [191 Paull [4 1 Jan. 16, 1973 s41 PRESSURE TRANSFER MECHANISM 3,510,217 5/1970 Cirimele et a1. ..355/l6 'hlH.PllM t'V, [75] Inventor gg oun am lew Primary Examiner-Robert P. Gremer Attorney-Lowhurst & Hamrick [73] Assignee: Photophysics, Inc., Mountain View,

Calif. [5 7] ABSTRACT [22] Filed: April 5, 1971 A pressure transfer mechanism is disclosed for apply- [21] Am). 6 130,948 ing evenly distributed pressure to a sheet of flexible photocopy paper overlying a planar surface of a photoconductor in an electrostatic photocopy'image --355/l6, 355/72, transfer station. The mechanism comprises a frame to 355/130 which the photoconductor is rigidly held and a mova- Cl- .603) ble plate mounted for movement respect to the 8] Field Search 118, frame and the photoconductor. A platen is disposed 95/68, 69 between the movable plate and the photoconductor which platen has a planar surface disposed adjacent [56] Rferellces Cited and substantially parallel the photoconductor planar surface. A first set of compression springs is sand- UNITED STATES PATENTS wiched between the movable plate and the frame. A 1,349,384 8/1920 Mclntire ..355/l28 second set of compression springs is sandwiched 1,744,621 1/1930 De Silva.... ....355/1 16 between the platen and the movable plate. 2,346,329 4/1944 Polhemus et al. ....355/1 18 3,499,709 3/1970 Uhlenberg ..355/3 8 Claims, 4 Drawing Figures Pmammm 16 I975 3.711.197

SHEET 1 BF 2 us /2 LI;

F PLATEN-ELECTRODE -Q) L PHOTOCOPY PAPER H TRANSPARENT SUPPORT MICHAEL H. PAULL ATTORNEYS BACKGROUND OF THE INVENTION This invention refers generally to electrostatic photocopiers, and more specifically to means for transferring an electrostatic image from the surface of a photoconductor to the surface of a sheet of photocopy paper overlying the photoconductor in an image transfer station.

In some types of electrostatic copies an optical image is projected onto one surface of a planar, photoconductive plate, and a sheet of photocopy paper is positioned against the other surface thereof. In such cases, the photoconductive plate typically comprises a transparent support upon one planar surface of which is deposited a thin layer of a transparent, electrically-conductive oxide such as Nesa or Nesatron. A layer of photoconductive material is in turn deposited on the layer of conductive oxide. Ideally, the exposed surface of the photoconductive layer would be absolutely planar as would be the sheets of photocopy paper placed thereon whereby abutment of the photoconductor and paper would be complete over their entire area of desired contact. In actuality, however, such perfection is rarely, if ever, achieved. This is largely due to cost factors. Thus, the transparent support is typically a sheet of ordinary plate glass, preferably Pyrex which is heat resistant. To use smoother glass such as that found in'optical astronomy would usually be cost prohibitive. In addition, in coating the glass substrate with the conductive oxide which provides a transparent electrode, and in coating the conductive oxide with photoconductive material the photoconductive plate must ordinarily be heatedThis application of heat introduced certain gradual, gross surface distortions in the nature of slight warping. Furthermore, the outer surface of the layer of photoconductive material itself has local, contour imperfections. As a consequence the exposed surface of most photoconductive plates are merely approximately rather than absolutely planar. Likewise, the flexible photocopy paper, which typically has a thin coating of dielectric plastic on the side facing the photoconductive plate, is only approximately planar when so supported. I

For proper transfer of an electrostatic image on the surface of the photoconductive plate to a surface of the dielectrically coated sheet of paper which has been placed in position overlying the plate, the entire areas of the two confronting surfaces should be in abutment. Otherwise, some areas of the electrostatic image may be transferred to a less extent than other areas. Whether such abutment under operating conditions is actual or virtual has been open to argument, but in any event the entire areas of these two confronting surfaces should be under uniform, convergent pressure for proper charge transfer to be effected.

In earlier electrostatic copiers of the type described, such evenly distributed pressure was achieved by sheer brute force. Such, however, did not provide satisfactory inasmuch as photoconductors in general use today are easily damaged when subjected to pressure in significant excess of one atmosphere. Later, such pressure distribution was achieved through the use of powdered spacers. Recently, vacuum devices, such as that disclosed by US. Pat. No. 3,506,348, were so used. However, in none of these devices of the prior art was a uniform, relatively low pressure achieved in asimple manner.

Accordingly, it is a principal object of the present invention to provide a pressure transfer mechanism for applying evenly distributed pressure to a flexible sheet of paper overlying a substantially planar surface of a photoconductor in an electrostatic photocopy image transfer station.

SUMMARY OF THE INVENTION sion springs is sandwiched between the movable plate,

and the frame. A second set of compression springs is sandwiched between the platen and the movable plate.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1. is a diagrammatical view of elements defining an image transfer station of an electrostatic photocopier in which a pressure transfer mechanism incorporating principles of the present invention may be used.

FIG. 2. is an elevational view of a pressure transfer mechanism incorporating principles of the present invention.

FIG. 3 is a side view of the apparatus shown in FIG. 2 taken in cross section along plane 33.

FIG. 4'is a plan view of the apparatus shown in FIGS. 2 and 3.

DESCRIPTION OF THE PREFERRED I EMBODIMENT with a dielectric material such as plastic whereby it may well retain a latent electrostatic image transferred thereon from the photoconductive plate. The photoconductive plate is seen to comprise a transparent support 15 such as plate glass upon which is coated a thin layer of a transparent conductive oxide 16 such as Nesa or Nesatron. A layer of photoconductive material 17 is in turn coated on the conductive oxide layer. Platen l2 and transparent, conductive oxide layer 16 of photoconductive plate 10 areelectrically coupled across a voltage source V and thus function as image transfer station electrodes. Platen 12 is also mechanically linked to a motor M Whereby it may be driven towards and away from photocopy paper 14 as indicated by arrows 18.

In operation, a sheet of photocopy paper is brought into the image transfer station with platen 12 spaced 7 from photoconductive plate 10. Motor M then drives platen 12 towards the photoconductive plate sandwiching photocopy paper 14 therebetween under'compressive force. With platen 12 and transparent electrode 16 coupled across a voltage source V an optical image is projected by means of light beam 19 through transparent support 15, transparent electrode 16 and onto photoconductor 17. The photoconductor converts the optical image on its side in contact with transparent electrode 16 to an electrostatic image on its side in contact with the photocopy paper. In this manner, the electrostatic image is transferred to the dielectri-' cally coated surface of the photocopy paper. Platen 12 is then driven by motor M away from photoconductive I plate and photocopy paper 14 is then removed. Al-

ternatively, the photoconductive platecould be driven away from the platen. Subsequently, the latent electrostatic image on photocopy paper 14 is toned and fixed sponge rubber124 arranged in a checkerboard pattern.

The ends of each sponge rubber column are preferably glued to base plate 20 and to support 22. A sheet'of conductive rubber 26 is stretched over the surface of planarsupport 22 facing outwardly from columns 24 and clamped to the sides of base plate 20 by means of screws 27 and bars 28.

The platen drive mechanism, which includes a pressure transfer mechanism, is seen to comprise two pillow blocks 30 mounted by means of screws 32 to a hollow frame 34. Shaft 36 is journaled through pillow blocks 30. Gear 37' is attached to shaft 36 which gear is in turn linked by a chain, not shown, to motor M. Two spaced plastic earns 38 are rigidly secured to shaft36 between pillow blocks 30. Four cylindrical posts 39 are mounted to frame 34. Four additional cylindrical posts 40 are mounted to base plate 20 of platen 12. Both posts 39 and'40 slidablyiextend through Oilite bushings in apertures within movable plate 42. Four relatively strong springs 44 are mounted about post 40 between the platen and movable plate 42, and four small noise abatement springs 46 are likewise mounted about posts 40 between movable plate 42 and shoulder screws 48. Four relatively weak springs 50 are mounted about posts 39 between frame 34 and movable plate '42. Herein by the terms strong and"'weak in describing spring strength is meant that for a given force a strong spring is-compressed a distance less than that of a weaker spring. Finally, two cam followers 52 are rotatablymounted to movable plate 42 in part by means of two nuts 54.

FIGS. 2 and 3 depict the platen in a raised 'position out of contact with photoconductiveplate 10 whereby motor M. This action will in turn cause cams 38 to revolve and push cam followers 52 downwardly in the direction of arrows 18. As the cam followers are rotatably attached to movable plate 42, the movable plate will likewise move downwardly compressing relatively weak springs 50. Platen 12 will then engage photocopy paper 14 and press it against photoconductive plate 10.1At this point, a slight further movement of the platen against the photocopy paper and photoconductive plate by rotation of earns 38 will cause compression of sheet 26 of conductive rubber, compression of columns 24 of sponge rubber, compression of relatively strong springs 40, and compression of relatively weak springs-50. Continued rotation of shaft 36 and cams 38 will permit movement of platenl2 away from photoconductive plate 10 by the face of the compressed springs and return the platen to its original position illustrated in the drawing with respect to frame i It should be understood that the described embodiment is merely illustrativeof applications of the invention and that many modifications may be made thereto without departure from thespirit and scope of the iiivention as set forth in the following claims.

What is claimed is:

1. A pressure transfer mechanism for applying evenly distributedpressure to a sheet of flexible photocopy paper overlying'a planar surface of a photoconductor in an electrostatic photocopy image transfer station,

said pressure transfer mechanism comprising: a frame to which said photoconductor is rigidly held; a movable plate mounted for movement with respect to said photoconductor;

a platen disposed between said movable plate and said photoconductor and having a planar surface disposed adjacent and substantially parallel said photoconductor planar surface;

first compressive spring meanssandwiche'd between t I said movable plate and said frame;

second compressive spring means sandwiched between said platen and said movable plate; and

.means incorporated with said frame for reciprocally v moving said movable plate, whereby downward motion of said movable plate moves said'movable plate against the pressure of said first compressive.

' claim 1 wherein said first compressive spring means comprises a first set of compression springs, and

wherein said second compressive spring means comprises a second set of compression springs.

' 3. A pressure transfer mechanism in accordance with' a second set of posts mounted to said platen and ex-' tending into said second set of apertures in said movable plate. l 4. A pressure transfer mechanism in accordance'with claim ,3 wherein said first set of springs are sandwiched claim 5 wherein each spring of said first set of springs is r substantially weaker than each spring of said second set of springs. I

7. A pressure transfer mechanism in accordance with claim 6 wherein said movable plate is rectilinear and has a geometric center, and wherein said first set of springs includes four springs located substantially equidistantly from said geometric center.

8. A pressure transfer mechanism in accordance with claim 7 wherein said second setof springs includes four springs located substantially equidistantly from "said geometric center a distance less than the distance said four springs of said first set of springs are located from said geometric center, i 

1. A pressure transfer mechanism for applying evenly distributed pressure to a sheet of flexible photocopy paper overlying a planar surface of a photoconductor in an electrostatic photocopy image transfer station, said pressure transfer mechanism comprising: a frame to which said photoconductor is rigidly held; a movable plate mounted for movement with respect to said photoconductor; a platen disposed between said movable plate and said photoconductor and having a planar surface disposed adjacent and substantially parallel said photoconductor planar surface; first compressive spring means sandwiched between said movable plate and said frame; second compressive spring means sandwiched between said platen and said movable plate; and means incorporated with said frame for reciprocally moving said movable plate, whereby downward motion of said movable plate moves said movable plate against the pressure of said first compressive spring means and moves said platen against said photocopy paper against the pressure of said second compressive spring means.
 2. A pressure transfer mechanism in accordance with claim 1 wherein said first compressive spring means comprises a first set of compression springs, and wherein said second compressive spring means comprises a second set of compression springs.
 3. A pressure transfer mechanism in accordance with claim 2 wherein said movable plate has first and second sets of apertures therein and wherein said mechanism further comprises: a first set of posts mounted to said frame and extending into said first set of apertures in said movable plate; and a second set of posts mounted to said platen and extending into said second set of apertures in said movable plate.
 4. A pressure transfer mechanism in accordance with claim 3 wherein said first set of springs are sandwiched between said movable plate and said frame about said first set of posts, and said second set of springs are sandwiched between said platen and said movable plate about said second set of posts.
 5. A pressure transfer mechanism in accordance with claim 2 wherein each spring of said first set of springs is of substantially the same strength, and wherein each spring of said second set of springs is also of substantially the same strength.
 6. A pressure transfer mechanism in accordance with claim 5 wherein each spring of said first set of springs is substantially weaker than each spring of said second set of springs.
 7. A pressure transfer mechanism in accordance with claim 6 wherein said movable plate is rectilinear and has a geometric center, and wherein said first set of springs includes four springs located substantially equidistantly from said geometric center.
 8. A pressure transfer mechanism in accordance with claim 7 wherein said second set of springs includes four springs located substantially equidistantly from said geometric center a distance less than the distance said four springs of said first set of springs are located from said geometric center. 